The eye forms from the interaction of the optic vesicle, an outpocketing of the ventral forebrain, with the surface ectoderm of the head. Contact between these tissues leads to the formation of the lens placode. The lens placode is the first step in lens formation and lens placode formation is required for the subsequent invagination of the optic vesicle to form the optic cup. Failure of these interactions leads to anophthalmia, microphthalmia or coloboma, which cause blindness or severely impaired vision. Despite their central importance in eye development, surprisingly little is known about the interactions between the optic vesicle and the lens-forming ectoderm. It is known that BMP4 from the optic vesicle and BMP receptors in the ectoderm are required for lens formation. Our recent data suggest that, in the ectoderm, BMP signaling and Pax6, a transcription factor required to make the lens, lie in the same pathway to promote lens formation. Homeodomain-interacting protein kinases (HIPKs) phosphorylate and activate Pax6 and deletion of Hipk1 and 2 prevents lens formation. Our studies will test the hypothesis that BMP signaling activates the HIPKs to promote Pax6 transcriptional activity and lens induction. Deletion of Pax6 in the ectoderm greatly reduced the extracellular matrix (ECM) between the optic vesicle and the ectoderm. This observation is consistent with an often overlooked hypothesis about the mechanism of lens placode formation, which we call the "restricted expansion" hypothesis. We propose to test this hypothesis to better understand the initiation of lens formation. In the process of our experiments, we observed that lens placode formation is accompanied by thickening of the distal optic vesicle to form what we call the "retinal placode." Disruption of lens placode formation also prevented the formation of the "retinal placode" and the invagination of the optic cup. Based on these observations, we formulated a simple model that explains the formation of the "retinal placode" and its invagination to form the optic cup. Testing this model will demonstrate the mechanism that coordinates the formation of the lens placode with the formation of the optic cup. Our studies of optic cup morphogenesis are being conducted in collaboration with Dr. Larry Taber in our Biomedical Engineering Department. With Dr. Taber, we will use time-lapse micro-OCT images to create a finite element model of optic cup invagination. We will then test this model using mutants in which optic cup formation fails or in which the ventral optic cup does not fuse, causing the formation of a coloboma. The experiments proposed in this application will identify and test the mechanisms that lead to the formation of the lens and optic cup and are required to produce a functional eye. PUBLIC HEALTH RELEVANCE: Project Narrative-Relevance to Public Health Failure of eye formation (anophthalmia), formation of a small, poorly-functioning eye (microphthalmia) and failure of the optic cup to close (coloboma) cause blindness or severe visual disability. Together, these defects are responsible for a substantial proportion of all childhood blindness. All three conditions are directly or indirectly associated with defects in communication between the two tissues the form the eye early in development, the optic vesicle and the surface ectoderm. The optic vesicle forms the retina and the surface ectoderm forms the lens. Our studies focus on how the lens-forming ectoderm responds to signals from the optic vesicle and how the surface ectoderm controls the formation of the retina. To accomplish these aims, we will determine the role in lens formation of two enzymes that are required for lens formation. We propose that these proteins link signals from the optic vesicle to the regulation of Pax6, a protein required for lens formation and lens-specific gene expression. We will also test a prediction that arose from our recent studies: the extracellular matrix between the optic vesicle and the ectoderm is required for both lens and optic cup formation. We will also use an advanced imaging technique to generate and analyze a computer model of optic cup formation in mouse embryos. Using this approach, we will also test how two growth factors control the shape of the optic cup to prevent coloboma formation. We expect these studies to provide the first comprehensive analysis of the tissue interactions in early eye development and to reveal the critical events required for eye formation. This will be the first step in preventing anophthalmia, microphthalmia and coloboma.